GRIPPER FEEDER FOR METAL STRIP

Abstract: A gripper feeder for metal strip characterized by comprising on a base (2): at least one pair of grippers (26, 26'; 126, 126'; 226, 226') for the engagement of the metal strip (42, 142) to be advanced; members (24, 12, 12', 48) for moving said grippers (26, 26'; 126, 126'; 226, 226') in a direction parallel to the axis of said strip (42, 142) and in the opposite direction; and means (34, 34'; 134, 134') for independently operating said grippers (26, 26'; 126, 126'; 226, 226') such that the gripper which moves in the direction of advancement of the strip (42, 142) is activated, whereas that which moves in the opposite direction is deactivated.

Description: GRIPPER FEEDER FOR METAL STRIP This invention relates to a gripper feeder for metal strip. Metal strip feeders are known for presses and machines in general in which the strip is subjected to particular operations as required. A known type of feeder of pneumatic operation uses two clamps acting transversely on the strip to be conveyed. One of these clamps is fixed, while the other is driven with reciprocating movement in a direction parallel to the longitudinal axis of the strip. In operation, the two clamps are operated alternately in a synchronized manner in the sense that when the fixed clamp is open the mobile clamp is closed onto the strip to advance it, whereas on termination of the advancement stroke of the mobile clamp the fixed clamp is closed and, after being opened, the mobile clamp is returned backwards to grip the metal strip further upstream and then advance it through a further distance when the fixed clamp is reopened. A drawback of this known feeder is that it is non- continuous and does not enable high operating speeds to be achieved. A further drawback is that it is extremely rigid, in the sense that it requires laborious manual action each time the advancement pitch of the metal strip is to be modified. A further drawback is that as it moves the metal strip by thrusting, it cannot be used for very thin strip. A further drawback is that it occupies the entire surface of the strip to be conveyed and does not allow it to be operated upon in that part engaged by the feeder. A further drawback is that it has a transverse dimension greater than the width of the strip, and for certain strip widths this dimension becomes excessive. A further drawback is that it cannot produce an advancement pitch greater than certain length. A roller feeder is also known comprising at least one pair of counter-rotating rollers between which the metal strip to be advanced is interposed. It substantially overcomes the drawbacks of known pneumatic feeders, and in particular is of continuous programmable operation. However it has other drawbacks, and in particular: - it engages the entire metal strip and therefore does not enable it to be subjected to other operations during the gripping; - it maintains the strip constantly engaged, and if this is curved in the horizontal plane or is inserted incorrectly into the feeder, transverse stresses of a progressively increasing extent arise and can be eliminated only by periodically slackening the grip between the rollers; - if the strip advancement is controlled by acting on the rollers, errors can arise because of the inevitable slippage between the rollers and the strip; if however it is controlled by acting on the strip itself these errors are not present, but the feeder then has a low advancement speed because of the need to correct errors deriving from inevitable slippage. Mechanical feeders with grippers controlled by the power machine positioned downstream of them are also known. In this case the grippers are driven with reciprocating movement and are reliable and fast. However they are extremely rigid in their performance and involve slow and difficult adjustment, which can be effected only by specialized personnel. The object of the invention is to obviate all the problems jointly and separately present in known feeders, by providing a feeder: - which is sustantially continuous; - which does not engage the entire surface of the metal strip and therefore enables it to be subjected to operations during its conveying; - which is fast; - which is programmable; - which is free from errors. All these ojects and further ones are attained according to the invention through a gripper feeder for metal strip as described in claim 1. Three preferred embodiments of the present invention are further described hereinafter by way of non-limiting example with reference to the accompanying drawings, in which: Figure 1 is a side view of a first embodiment of a gripper feeder according to the invention; Figure 2 is a cross-section therethrough on the line II-II of Figure 3; Figure 3 is a plan view thereof on the line III-III of Figure l ; Figure 4 is a side view of a second embodiment thereof; Figure 5 is a cross-section therethrough on the line V-V of Figure 6; Figure 6 is a plan view thereof on the line NI-VI of Figure 4/ Figure 7 is a side view of a third embodiment thereof; Figure 8 is a cross-section therethrough on the line VIII- VIII of Figure 7; and Figure 9 is a plan view thereof on the line IX-IX of Figure 7. As can be seen from the drawings, the gripper feeder for metal strip according to the invention comprises, in the embodiment shown in Figures 1 to 3, a base 2 on which there are mounted two longitudinal rails 4,4' for guiding two slides 6,6' on which two carriages 8,8' are mounted. Each of the carriages 8,8' is provided with a threaded bush 10,10' in which there engages a threaded rod 12,12' situated in a position overlying the corresponding guide 4,4'. The two rods 12,12' are threaded in opposite directions. Each threaded rod 12,12' is supported by a pair of supports 14,14' fixed to the base 2. Specifically, each rod 12,12' is supported by the support 14 exactly at its left hand end with reference to Figures 1 and 3, whereas it extends beyond the support 14' at its right hand end, where it carries a toothed wheel 16,16' coupled via a toothed belt 18,18' to another toothed wheel 20,20' keyed onto the exit shaft 22 of a direct current electric motor 24 mounted on the base 2 between the two threaded rods 12,12'. Each carriage 8,8' supports a gripper 26,26' which is slidable along a dovetail rail 28,28' arranged transversely, ie perpendicular to the axis of the threaded rods 12,12' , and of which the movements are controlled by a respective mechanical actuator 30,30'. Each gripper 26,26' comprises a fixed jaw rigid with the slide slidable along the corresponding rail 28,28', and a movable jaw 32,32' driven relative to the fixed jaw by a pneumatic actuator 34,34' of vertical axis. On the supports 14,14' for the threaded rods 12,12' there are also mounted transverse dovetail guides 36,36' along which there slide pairs of carriages 38,38' supporting rollers 40,40' of vertical axis with their lateral surface comprising a groove for engaging and guiding the longitudinal edge of the metal strip 42 to be advanced. The carriages 38,38' are driven along the respective guides 36,36' by mechanical actuators 44,44'. The operation of this first embodiment of the feeder according to the invention is as follows: an adjustment is firstly made to adapt the machine to the width of the strip 42 to be fed; this adjustment requires operating the actuators 30,30' which adjust the distance between the grippers 26,26', and then the actuators 44,44' which adjust the distance between the guide rollers 40,40' of each pair. Having made this preliminary adjustment, the machine is ready to operate. The electric motor 24 is powered to rotate in one of the two directions of rotation, with the result that because of the particular coupling between this latter and the two threaded rods 12,12', these are rotated in the same direction. However, as their threads are in opposite directions, their identical rotation causes the two carriages 8,8' to slide in the opposite direction along the respective rails 4,4', with consequent sliding in the opposite direction of the two grippers 26,26' mounted on said carriages. At the same time an activation command is fed to the gripper 26, which during this stage moves in the same direction as the predetermined direction of advancement of the metal strip 42, indicated by the arrow 46 in the drawings, and a deactivation command is fed to the gripper 26' which moves in the opposite direction. When the gripper 26 has practically reached its front end-of-travel position along the respective guide 4 and the gripper 26' has reached its rear end-of-travel position along the respective guide 4', the direction of rotation of the electric motor 24 is reversed while at the same time a deactivation command is fed to the actuator 34 of the gripper 26 and a deactivation command is fed to the actuatore 34' of the gripper 26', so that also in this case the gripper which moves in the same direction as the predetermined direction of advancement of the metal strip 42 grips said strip and the gripper which moves in the opposite direction disengages from it. This alternation in the direction of rotation of the motor 24 and the alternation in the activation commands for the two grippers results in unidirectional advancement of the metal strip 42, this advancement having an intermittency which can be made to approach continuity by suitably controlling the various intervention times. From the aforegoing it is apparent that the gripper feeder according to the invention is considerably more advantageous than conventional feeders, and in particular: - it grips the strip only along a longitudinal edge thereof, this on the one hand leaving the remainder of the strip free for possible operations and on the other hand resulting in a small overall size independent of the strip width; - it grips the strip at successive points, so allowing any incorrect dragging due to strip curving or to incorrect insertion into the feeder to be corrected; - it provides effective guide action for the strip along both edges; - it ensures reliable gripping of the metal strip 42 without any slippage between this and the grippers, so ensuring its correct advancement by controlling the motor 24 which operates the threaded rods 12,12'; in this manner, electronic and hence programmable advancement control is made possible in a like manner to conventional electronic roller feeders, while at the same time mechanical and hence slippage-free gripping is provided in a like manner to mechanical or pneumatic feeders. in the embodiment shown in Figures 4 to 6, in which corresponding parts carry the same reference numerals, the general principle of gripping the metal strip 42 alternately on one and the other longitudinal edge by a gripper which is kept engaged during the working stroke and opened during the return stroke does not change, however a different system for moving the two grippers 26,26' longitudinally in alternate directions is provided. Specifically, the two carriages 8,8' which support the two grippers are fixed to a single toothed belt 48 passing about two toothed deviation pulleys 50,50' of vertical axis, of which the pulley 50 is idle and the other is keyed onto the exit shaft of a direct current motor 24 which is rotated alternately in the two directions, in a like manner to the motor 24 of the preceding embodiment. This embodiment has all the advantages of the preceding, and in addition represents a more economical construction because of the smaller number and lower cost of the component used for moving the grippers 26,26'. In the embodiment shown in Figures 7 to 9, two transverse grippers are provided acting on the entire length of the metal strip 142. The lower jaw of each gripper 126,126' lowerly protrudes in a carriage 108 provided with a threaded bush 110 in which there engages a threaded rod 112 realized in two portions threaded in opposite directions. The threaded rod is driven, as in the embodiment of Figures 1-3, by a direct current electric motor 124. Each gripper comprises a fixed jaw rigid with the carriage and a movable jaw driven relative to the fixed jaw by pneumatic actuator 134,134' of vertica axis. It being understood that the general principle of gripping the metal strip by a gripper which is kept engaged during the working stroke and opened during the return stroke, it is obvious that, due to the opposite threads of the rods 112, while a gripper 126,126' carries out the working stroke, the other gripper 126',126 carries out the return stroke. This embodiment enables to obtain a more reliable operative precision since the operating obtained through one threaded rod eliminates the possible plays. Furthermore the entire width shaped gripper enables to be adapted to metal strip of different width without however laterally adjusting the position of the grippers. In the embodiment shows in Figures 10 to 12 the gripper 226,226' are positioned on both sides of the metal strip and are connected, as in the previous embodiment, to only one rod 212, provided with two opposite threads, so to the stroke of a gripper in one direction it corresponds the stroke of the other gripper in the opposite direction. In a further embodiment (not shown on the drawings) the two grippers are positioned on both the sides of a toothed belt with its longitudinal portions which are parallel to the longitudinal axis of the metal strip. Also in this embodiment devices are foreseen which enables the clamping by the gripper during the working stroke and cause their opening during the stroke in opposite direction. This embodiment presents the advantage of carrying out the clamping of the metal strip only in correspondence of one longitudinal edge thereof, and this on one hand allows to let free the remaning portion of the strip and on the other hand has a limited encumbrance and not related to the width of the same strip.

Claims: C L A I M S 1. A gripper feeder for metal strip characterised by comprising on a base (2) : - at least one pair of grippers (26,26'; 126,126'; 226,226') for the engagement of the metal strip (42,142) to be advanced; - members (24,12,12' ,48) for moving said grippers (26,26'; 126,126'; 226,226') in a direction parallel to the axis of said strip (42,142) and in the opposite direction; and - means (34,34'; 134,134') for independently operating said grippers (26,26'; 126,126'; 226,226') such that the gripper which moves in the direction of advancement of the strip (42,142) is activated, whereas that which moves in the opposite direction is deactivated. 2. A feeder as claimed in claim 1 characterized by comprising at least one pair of grippers positioned on both sides of the metal strip. 3. A feeder as claimed in claim 1 characterized in that each gripper of the pair (126,126') extends at least for the entire width of the strip. 4. A feeder as claimed in claim 1, characterised in that each gripper (26,26'; 126,126'; 226,226') is mounted on a carriage (8,8',108) slidable along a guide rail (4,4') apllied to said base (2). 5. A feeder as claimed in claim 1, characterised in that each gripper (26,26'; 126,126'; 226,226') comprises a fixed part rigid with the respective carriage (8,8',108) and a movable part (32,32'; 132,132') operated by an actuator (34,34'; 134,134') . 6. A feeder as claimed in claim 1, characterised in that each gripper (26,26') is mounted on a slide slidable along a horizontal guide rail (28,28') arranged perpendicular to the axis of the metal strip (42) . 7. A feeder as claimed in claim 6, characterised in that an actuator (30,30') is associated with each gripper (26,26') for its movement along the respective guide rail (28,28'). 8. A feeder as claimed in claim 1, characterised in that on the base (2) there are. applied pairs of rollers (40,40') of vertical axis having in their lateral surface a circumferential groove for engaging and guiding the corresponding longitudinal edge of the metal strip (42) . 9. A feeder as claimed in claim 8, characterised in that at least one roller (40,40') of each pair is movable relative to the base (2) in a direction perpendicular to the axis of the metal strip (42). 10. A feeder as claimed in claim 9, characterised in that the two rollers (40,40') of each pair are mounted on slides movable along a guide rail (36,36') arranged perpendicular to the axis of the metal strip (42) on supports (14,14') rigid with the base (2) . 11. A feeder as claimed in claim 10, characterised in that an actuator (44,44') is interposed between the slide of each guide roller (40,40') and the respective support (14,14'). 12. A feeder as claimed in claim 3, characterised in that each carriage (8,8',108) is provided with a threaded bush (10,10',110) engaged by a rod (12,12',112) having two portions threaded in opposite directions and rotated by a single electric motor (24,124) powered alternately in the two directions of rotation. 13. A feeder as claimed in claim 12, characterised in that to the base (2) there are applied two rods (12,12') threaded in opposite directions and coupled to the exit shaft (22) of said electric motor (24) by belts (18,18') and pulleys (16,16',20,20') . 14. A feeder as claimed in claim 3, characterised in that each carriage (8,8') is rigid with one of the two rectilinear portions of a toothed belt (48) passing about two pinions (50,50') of vertical axis, one (50') of which is associated with an electric motor (24) driven alternately in the two directions of rotation.

Inventors: ZANETTE DONATO, ZANETTE, DONATO
Applicants: DALCOS S R L, ZANETTE DONATO, DALCOS S.R.L., ZANETTE, DONATO
Application year: 1994
Main classification: B21D43
IPC codes: B21D43